In plain language
Extended-gamut YCbCr allows colour values outside the boundaries of the old Rec.709 space, so more saturated colours can be described. It arrived with HDMI 1.3 alongside deep colour.
Why it matters in your setup
In practice, not much any more. Content using xvYCC is rare, and the wide-gamut job is now done by BT.2020 with HDR metadata. It survives on specification sheets as a compatibility item.
It is worth recognising the name so you do not mistake it for something you are missing. If a device lists xvYCC support, that is a legacy capability, not a modern HDR feature.
What the DR HDMI 8K does with it
The DR HDMI 8K lists xvYCC colour support in its specifications alongside deep colour and 3D. For current content the capabilities that matter are BT.2020, the HDR modes and the Dolby Vision data block — all of which the unit controls directly through its EDID flags.
Need the hardware?
Open the DR HDMI 8K product page on HDfury.uk.